At strap buckles intended for interconnecting two strap or belt parts, e.g. in clothes, leisure equipment such as safety jackets, packages etcetera, it is a desire, that the lock has a self-locking function, i.e. that it arrests the strap part arranged therein for as long as the lock is unaffected by external forces.
This self-locking is commonly effected by a locking member arranged in conventional manner upon a shaft, which locking member is biased by a spring to be pressed against locking position, when unaffected.
This, being the predominant type of clamps or strap buckles of this kind, has drawbacks in that they consist of at least three main parts, which at assembly require a considerably cost-increasing manual work, as the three main parts, one of which is usually a metallic spring, can hardly be assembled in automatic machines. The spring furthermore must be of a high-quality metallic material in order not to suffer from fatigue after a period of use or becoming damaged e.g. from salt water or at washing together with an article of clothing.
From U.S. Pat. No. 1,398,126 is earlier known a clamp, wherein this common principle has been abandoned and this clamp comprises a frame-shaped holder with a shaft arranged between the opposite inner long sides of the frame, about which shaft is pivotably supported a double-armed locking member, which is arranged to cooperate with one end gable of the frame, thereby locking a part of a strap situated between the locking member and said end gable, and which locking member under actuation of an external force is pivotable about the shaft against the action of a resilient member. The transverse shaft is located at the side of the holder facing away from the end gable cooperating with the locking member and it has an oval cross-section. The resilient member consists of a central stamped-out tounge in the locking member, which on the other side of the shaft projects outside the holder. When opening the locking member the bigger diameter of the oval shaft hereby will force the tounge away from the other portions of the locking member and produce a force, striving to pivot the locking member to locking position. Due to the open design there however is a risk that the locking member can fall off the shaft, when the member is in open position. It furthermore must be considered highly probable that the stamped-out tounge after a rather small number of opening and closing movements may be deformed and/or fatigued so much that it can not guarantee a satisfactory locking effect. The design, where one arm of the locking member projects outside the frame, finally means that particular conditions are required for a strap buckle of this type to be locked and opened resp. when in stretched condition, as one of the two locking member arms at opening or locking movement must move past the plane of the holder, inwards against the object around which the strap is locked. This is impractical but possible when it concerns soft, deformable objects, as e.g. the waist of a human being, but not if the surface upon which the strap is arranged is stiff, undeformable.